Acoustic insulation design begins by understanding the differences between air-borne noise and structure-borne noise. There are other important considerations, too.
Noisy equipment can cause hearing loss and result in violations that carry fines and other penalties. In North America, regulatory agencies such as OSHA, NIOSH and the Canadian Center for Occupational Health and Safety (OHS) establish workplace limits for noise exposure. Yet the fact remains that noise and hearing loss are the second most prevalent self-reported work-related injury, according to the Hearing Research Laboratory at the University of Ottawa.
Noise can also affect perceptions of product quality. That’s why some potential car buyers listen to how a vehicle’s door sounds when it closes. In a sports car, engine noise suggests speed and power. In a tractor, dump track, or military vehicle, loud engine sounds within the cab are unwanted. For technical buyers and design engineers then, noise mitigation can be about enhancing worker safety, ensuring regulatory compliance, improving the customer experience – or all of the above.
Acoustic insulation is essential, but what are some design considerations? In other words, what do buyers and designers need to know?
Acoustic Insulation Design: Air-Borne Noise and Structure-Borne Noise
For starters, it’s important to understand how sound is transmitted. Noise, which can be defined simply as any unwanted sound, doesn’t always travel directly through the air to human ears. In the case of an equipment enclosure, thin metal or plastic walls separate people from equipment. These barriers provide some noise mitigation, but they provide better environmental resistance than they do sound dampening. Even small holes or gaps in a metal or plastic enclosure can allow significant acoustic leakage.
Within the equipment enclosure itself, noise is also problematic. Because the enclosure causes sound waves to reflect inward rather than project outward, structure-borne noise can induce vibrations. For example, a pump that’s next to an enclosed fan or electric motor can cause the fan or motor to vibrate, and to transmit vibrations to nearby frames, supports, and shields. These vibrations contribute to noise levels within the enclosure, and can damage system components that lack adequate supports.
Acoustic Insulation Design: Sound Dampening and Sound Absorption
When specifying acoustic insulation then, material buyers and product designers need to determine whether they need sound dampening materials, sound absorbing materials, or both.
Let’s look at the difference.
- Sound dampening materials prevent sound from leaving an enclosed space such as an engine bay or equipment enclosure.
- Sound absorbing materials absorb sounds within a confined space and can help to protect system components within.
Typically, sound dampening materials are dense, rigid, and heavy. By contrast, sound absorbing materials are soft and sponge-like. That’s because, much like a sponge soaks up water, sound absorbing materials “soak up” sound. With an insulation sandwich, however, you can incorporate both types of materials. To learn more about these specialty insulation structures, read this recent blog entry.
Application Environments and Noise Mitigation
For all types of acoustic insulation – including sandwich-like structures – technical buyers and product designers must also consider the application environment. As with other materials, compound selection is about asking and answering questions. For example:
- Does the material need to withstand extreme heat or extreme cold?
- Is there exposure to rain, snow, wind, or sunlight?
- Does the application require an FDA-approved or military-grade material?
- Will the compound come into contact with oils, solvents, fuels, and other fluids?
Buyers and designers must also ask and answer questions that are specific to acoustic insulation. For example, what is the range of frequencies that require sound dampening or sound absorption? Some acoustic materials are designed for high frequencies. Others are suitable for low frequencies.